Fiber optic communication is an emerging method of transmitting information from a source (transmitter) to a destination (receiver) using optical fibers as the communication channel. WDM-PON is an optical technology for access and backhaul networks. WDM-PON uses multiple different wavelengths over a physical point-to-multipoint fiber infrastructure that contains passive optical components. The use of different wavelengths allows for traffic separation within the same physical fiber. The result is a network that provides logical point-to-point connections over a physical point-to-multipoint network topology. WDM-PON allows operators to deliver high bandwidth to multiple endpoints over long distances. A PON generally includes an optical line terminal located at a service provider central office (e.g., a hub), a remote node connected to the central office by a feeder fiber, and a number of optical network units or optical network terminals, near end users. The remote node demultiplexes an optical signal from the central office and distributes the demultiplexed optical signals to multiple optical network terminals along corresponding distribution fibers. Time-division-multiplexing (TDM) is a method of transmitting and receiving independent signals over a common signal path by using different, non-overlapping time slots. Time wavelength division multiplexing (TWDM) uses both time and wavelength dimensions to multiplex signals. Color-less optical network units (ONUs), which are based on tunable laser and suitable driving topologies, are critical components for flexible WDM/TWDM-PON system architectures. The laser driving circuit in the ONU is the component to generate the upstream optical signal. To meet the WDM/TWDM-PON system requirements, the driving circuit has to guarantee the optical output has not only enough power and modulation magnitudes, but also short burst switching times and minimum wavelength drifts.